1. Field of the Invention
The present invention relates to a speech recognition apparatus, a speech recognition method, and a recording medium having a speech recognition software program recorded thereon, and, more particularly, to a speech recognition apparatus, a speech recognition method, and a recording medium having recorded thereon a speech recognition software program, which, as a result of being provided with a rejectable word dictionary that stores rejectable vocabulary words in addition to a recognition word dictionary that stores recognition vocabulary words, is capable of rejecting background noise, background speech, or utterances of out-of-recognition vocabulary words and outputting recognition results only when recognition vocabulary words are uttered.
2. Description of Related Art
Speech recognition apparatuses using a speech recognition engine as a means of accepting input from a user in order to recognize user utterances (speech) and accept them as input to the system have been known in the past. For example, such speech recognition apparatuses have already been put to practical use in information providing systems, including speech portals, car navigation systems, etc.
Incidentally, such speech recognition apparatuses suffered from the problem that, for instance, depending on the environment of use of the information providing system provided with such speech recognition apparatuses, background noise, background speech, and the like may be misrecognized as recognition vocabulary words. Moreover, there is the problem that words might be misrecognized as recognition vocabulary words when the user utters out-of-recognition vocabulary words.
To eliminate such problems, a speech recognition apparatus has been proposed which, in addition to a recognition word dictionary that stores recognition vocabulary words, is provided with a rejectable word dictionary that stores rejectable vocabulary words. Specifically, this speech recognition apparatus, along with computing the degree of similarity between the input speech and the recognition vocabulary words, computes the degree of similarity between the input speech and the rejectable vocabulary words. As a result of computing the degree of similarity, recognition vocabulary words are outputted as a recognition result when the degree of similarity of the recognition vocabulary words is higher than the degree of similarity of the rejectable vocabulary words. On the other hand, it rejects input speech when the degree of similarity of the recognition vocabulary words is smaller than the degree of similarity of the rejectable vocabulary words. Thus, storing background noise, background speech, or out-of-recognition vocabulary words as rejectable vocabulary words in the rejectable word dictionary makes it possible to prevent background noise, background speech, or out-of-recognition vocabulary words from being misrecognized as recognition vocabulary words (see, for instance, JP 2002-372988A or JP H10-49190A).
However, if the recognition vocabulary words and rejectable vocabulary words in such a speech recognition apparatus are, for instance, identical or similar, user utterances get mistakenly rejected despite the fact that the user utters recognition vocabulary words when the degree of similarity of the rejectable vocabulary words is higher than the degree of similarity of the recognition vocabulary words.
Thus, in the speech recognition apparatus disclosed in JP 2002-372988A, a rejectable word removal unit removes rejectable vocabulary words that are the same or similar to the recognition vocabulary words stored in a recognition word dictionary from a rejectable word database storing a comprehensive set of rejectable words. The rejectable word removal unit generates a rejectable word dictionary by storing the residual rejectable vocabulary words remaining in the rejectable word database in a rejectable word dictionary. This makes it possible to prevent user utterances from getting mistakenly rejected when the user utters recognition vocabulary words.
However, the following problems arise in connection with the configuration disclosed in JP 2002-372988A mentioned above.
Namely, in the speech recognition apparatus of JP 2002-372988A, the rejectable word dictionary has to be updated by removing rejectable vocabulary words that are the same or similar to the recognition vocabulary words from the rejectable word database and storing the residual rejectable vocabulary words remaining in the rejectable word database in the rejectable word dictionary whenever changes are made to the recognition vocabulary words stored in the recognition word dictionary. For this reason, manual and time-consuming operations are required to update the rejectable word dictionary when changes are made to the recognition vocabulary words stored in the recognition word dictionary.